The polyphenylene ether resins are a family of engineering thermoplastics known to be useful with other polymers such as alkenyl aromatic resins to form compositions which are extrudable and moldable into various articles of commerce. The polyphenylene ether resins are described in the patent literature, for example, in U.S. Pat. Nos. 3,306,874 and 3,306,875 (Hay), and U.S. Pat. Nos. 3,257,357 and 3,257,358 (Stamatoff). Blends of polyphenylene ether resin and styrene polymers are disclosed by Cizek in U.S. Pat. No. 3,383,435.
It is also known that polyphenylene ether resin blends can be made more flame retardant by the addition of agents effective for that purpose. Flame retardant polyphenylene ether--polystyrene compositions are described, for instance, in Lee, Jr., U.S. Pat. No. 4,203,931, in which a halogenated aromatic, for example, tetrabromobenzene, is proposed as a suitable agent; and in Haaf, et al., U.S. Pat. No. 4,355,126, in which aromatic phosphates and halogenated aromatics are listed. All of these compositions are thermoplastic by nature, being softened upon heating followed by hardening when cooled.